Ship propulsion system



e. 1932- w. SCHAELCHLIN 7 ,861,454

' SHIP PROPULSION SYSTEM Filed Feb. 6, 1929 '0 I-ZIJIKIJILm' INVENTOR Wd/fPl Sc/zae/ch/M. i

BY 2 2 "'47 AETTORNEY forming e systermwliich naturally provides UNITED STATES PATENT OFFICE WALTER I OI UBG, PENNSYLVANIA, ASSIGNOB TO wns'rm'm HOUSE ELEGI'BIC & KANUILGIUBIHG comm, A CORPORATION OI PENNSYL- smr rnormrou m Application fled I'ebruary a, 1m. mm m. sauna.

My invention relates, generally, to electricpower systems, andmore articularly, to electric power-systems for s ip propulsion.

. Heretofore,-ship propulsion systems have been commonly employed which would essure the delivery of very high propeller tor ues for taking care of various operating con itions, common to ship propulsion. For example, in maneuvering and operating in rough sees, it becomes highly important that suflicient propeller torque be provided to take care of the sudden and frequent rlemends which are imposed upon the power system. Usually, induction motors, having high torque 'charscteristics, have been employed in connection with synchronous generators,

the desire& torque enfl power characteristics, but at e sacrifice of operating eficiency. Also the low operating power factor or on incluctionrnotor of this type required that the size of both the motor and. the generator be increased in order that the ineficient encl low power factor system lee cepslole oi olevelcping suiiicient power. Systems of this kind are objectionable from both the stenilpoint of" cost and oiled weight ofthe propulsion. system. lln light ships such as cruisers, guerdcutters end tlre'lilre the consirleretion of weight becomes important since lightness is ct leost one important factor which must be considlereol to insure high speerl operation and ehility to maneuver quickly.

The object I of my invention generelly statecl, is to provide on electric ship-propel sion system which shell be simple encl sill cientin operation, cncl capable of being eco= noniicelly inenuiectnred and installed.

A more specific object of my invention is.

to provide forcorrelstingtlie etlinstrnent of the excitation of an interconnectelsynchro nous propulsion motor and synchronous gen eretor to maintain system stability in corclence with the load on the system.

Another object of my invention is to pro vide for operating a ship propulsion system comprising. an interconnected synchronous generator and synchronous motor to maintain unity power factor of the system throughout its range of operation.

A further object of my invention is to proride, in a ship-propulsion system comprisin an interconnected synchronous generator on synchronous motor, for varying the kilowatt loml capacity of the system to chen e the degree of system stability Without clist-urbin or changing the operating power factor 0 the system.

@ther objects of my invention will become eviclent from the following description taken in conjunction with the drawing in which:

Figure 1 is s (liegremmetie View of an electric ship-propulsion system arranged in sccorclance with end emboclying the features oi my invention.

Fi s. 2 end 3 ere plan ernl side views respectively or": e preferred arrangement of the generator motor lieu-controlling rliec: stats which are shown schematically in Fig. Lfilltil 2 is n sequence chart showing the method of operation of the field-controlling switch sliown 1.

Referring now to l oi? the drawing, ll? designates oenerelly on electric motor which rosy be utilized to actuate s ship propeller 31.. in this instance an alternatingurrent synchronous motor provided wit winrling l2, snol fielcl windings l3;

reel. order to control the operstion of the propulsion motor 10, synchronous generotor st-stor winclingrs l5. and fielo. windings 3.6, is provitleai ror supplying power motor o variable frequency encl voltege.

The synchronous generator 14 may be driven loy means of any snitelole type of prime mover capable of leaving speed reeclily veriecl to the frequency or we goneretor oncl consequently the speecl of operation. oi? the propulsion motor 10. in this eniloorliment of tlie invention. e steam turbine l? oil any well known type is shown and connected :Zor driving the generator 14.

ince the means for controlling the opereting speed of the turbine 1? are Well lmown and. term no part of this invention, it has been deemed unnecessary to illustrate them.

As shown the stator windings 12 and 15,

ill)

power w ch, in this instance, may be represented by line conductors 24, 25 and 26, concontrol switch '23 m the reverse direction to stituting a three-wire double-voltage system.

In this embodiment of the invention a manually operated switch 27 is provided for controlllng the main-excitation circuits for the generator and the motor fields. As shown, the switch 27 is provided with main contact members 28 and 29, and auxiliary contact members 31 and 32. In this instance, the auxiliary contact members 31 and 32 are utilized to establish discharge circuits for the field winding 16 and 13, when the field switch 27 is in the open position as illus-. trated.

In order to provide for varying the exciting current which is supplied to the generator field winding'lfi, and motor field winding 13, a plurality 'of field rheostats desi nated nerally as 33 and 34, are provide In t e operation of the system the generator 16 may be started by setting the prime mover 17, in operation in the usual manner, with the field switch 27 and reversing switches 21 and 22, in' the open position as shown.

In order to start the propulsion motor 10 with a minimum amount of power demand upon the generator, the main circuit between the generator and motor ma be established by the closure of either the reversing switches 21 and 22, before the generator voltage is established. Therefore, if it is desired to operate the pro ulsion motor in the forward direction, t e control switch 23 may I be actuated into the forward position to enge contact members 35, which connects t 0 operating coil of the reversing switch 21 across the line conductors ;and 26 through a circuit comprising conductors 36 and 37. Likewise, the reversing switch 22 may be closed to connect the propulsion motor for reverse operation by actuating the contact members 38. t will be readily understood that by connecting-the motor and generator together before the generator voltage is .built up, the

- motor will-be started and accelerated as an ""tion" of the generator contact members and movable segments for controlling the excitation circuits, is illustrated. I

Referring to Fig. 4 it will be observed that when the field control switch 39 is set in the off position which is designated, in this instance, by the legend Securethe contact members 41 and 42 are bridged b their corresponding contact se ents 3 and 44. Since these contact mem ers are bridged, the field discharge circuits for the motor 10 and generator 14 are maintained when the switch 27 is actuated-to close the main field circuits, the field discharge circuits formerly established by the contact members 31 and 32, of the switch 27, bein interrupted in response to the operatlon o the switch to close contact members 28 and 29. As shown the field discharge circuit for the generator field 16 extends from one side of the field winding 16, through the discharge resistor 45, conductors 46 and 47 ontact members 41 bridged by the segme t 43, conductor 67, a section of the resistor 48, conductor 49, contact members 28 and conductor 51 to the opposite side of the field winding 16. Likewise the discharge circuit for the motor field win ing 13 may be traced from one side of the field windin '13, throughthe discharge resistor 52, con uctors 53, and 54, contact members 42 bridged by the segments 44, conductors 55, contact members 29 of the switch 27, and conductors56 to the opposite side of the field winding 13.

In power ms of this character it is highly desira 1e that the generator excitation be controlled in such manner as to provide for causin the generator to quickly develop its ra volta in order to get the s stem in operation wlth the least possible elay. Therefore, in this instance, provision is made for subjecting the field winding 16, of the'generator 14, to an initial vo tage which is equal to its rated voltage and then to a double voltage in order to produce a field forcing efiect.

Therefore, upon the movement of the field control switch 39 to its first running 'tion the pairs of contact members, 57 an 58, are bridged by the contact segments, 59 and 60,

respectivel The'brid 'ng of contact memd 58, establ 5% here 57 an i esan energizing circuit for the generator field windmg which extends from the line conductor 26 through contact members 57 conductor 61, field winding 16, conductor 51, contact members 28, conductor 49, resistor 48, conductor 62, field rheostat 33, conductor 63, and contact members 58 of the field control switch 39 to the line conductor 25. Simultaneously, with the establishment of the field excitation circuit, a

air of contact members 41, were disengaged y the "contact segment 43 to interrupt the field discharge circuit formerly established by the bridging of contact members 28 of the switch 27. Therefore, it will .be readily understood that the generator field winding 16 is subjected to an initial voltage carried by the line conductors 25 and 26, which in this instance,is the rated voltage of the field.

Movement of the field control switch 39 to the second position bridges the pair of contact members 64 without interrupting the circuit previously established by the bridging of contact members, 57 and 58 and, establishes the second energizing circuit for the generator field, which subjects it to the full double-voltage of the excitation source. This circuit may be traced from line conductor 24 through the contact members 64, bridged by segment 65, conductors 66 and 67 resistor 48, conductor 49,'contaet members 28, conductor 51, generator field winding '16, conductor 61, and contact members 57 to the line conductor 26.

Further operation of the field control switch 39 effects a disengagement of the contact segment from the contact members 42 to interrupt the field discharge circuit of the motor and establish its energizing circuit through the bridging of the pairs of contact members 68 and 69 by the contact segments 44 and 73, respectively. As shown this circuit extends from line conductor 24 through contact member 68, bridged by segment 44, conductor 55, contact members 29 of the switch 27 conductor 56, motor field winding 13, conductor 71', field rheostat 34, conductor 72, contact member 69,.bridged-by segment 73 to the line conductor 26. I It will be readily understood that-the energization of the field winding13 causes the synchronous motor 10 to automatically pull into synchronism with the generator 14, which is operating at a speed determined by the speed of its driving turbine 17.

When the field control switch 39 is actuated to its last, or running position .desig nated as 11", it disengages-the contact segment 44 from contact members 42 to interrupt the double voltage excitation circuit to the generator field winding 16, while the remaining contact members 57 and 58 are still bridged to maintain the rated voltage excitation circuit. It will be evident that duragain to rated voltage, the. original rated tact segment 75 to connect the contact arm 76 of the field rheostat 33 to the line conductor 25 thereby to render the rheostat 33 efiective to vary the generator excitation. As described hereinbefore this circuit extends through the rheostat 33, conductor 63, and contact members 58 to the line conductor 25.

In order to control the power factor of the system, propulsion motor 10 and the enerator 14 are'designed to have substantially the same electrical characteristics. found, in practice, that two synchronous machines operating in this relation may be caused to operate at any desired power factor depending upon their relative excitations, provided that the short-circuit characteristics of the two machines are substantially the same. In other words, if the internal characteristics of the machines are such that for equal load currents the internal drop of potential is practically the same, asetting of the field excitation to provide a predetermined power factor for one speed and load will cause the ower factor to remain the same over the who e range of operation. In this instance, unity power factor operation is the most desirable since, at this power factor, the system from the It has been will operate at its maximum efiiciency and deliver a maximum amount of power. It will be readily understood that once the field excitations of the motor and generator have been adjusted to provide unity power factor operation, it is necessary to maintain this ratio between the generator, and motor excitations in order that this power factor condition may not be disturbed when the voltage of the generator is varied by changing its excitation. Therefore, in this embodiment of the invention, provision is made for connecting the generator field rheostat'33 and motor field rheostat 34 together after they have once been properly ad usted in order that the movement of one will efi'ect a corresponding movement of the-other. Referring to Figs. 2 and 3, it will be observed that this function is accomplished by means or a plurality of sprocket chains-77 and 7 8 which connect the o crating shaft of each rheostat to a clutch s aft 79, which is provided with a toothed clutch 80, which may e operated by a lever 81 to clutch the sprocket wheels 82 and 83 which are carried by the shaft 79 into any desired relative position. The rheostats 33 and 34 are provided with operating wheels 84 and 85, respectively,

of controlling the stability of the system with I a minimum amount of adjustment of the field excitations. It will be readily understood that a wer system of this character when in operatlon is capable of developing a predetermined maximum kilowatt output, This maximum kilowatt output is determined for a given pair of machines by the degree of field excitation and is a measure, or indication, of the stability of the system. When this point of maximum kilowatt output is passed, the system has passed its maximum stability point and the motor will drop out of synchronism with the supply generator, due to the fact that the synchronizing power between the two machines is no longer suflicient to maintain them in their pro r relative phase position. Therefore, it Wll be readily understood that a change in the excitation of the generator efiects a correspondin change in the maximum kilowatt load whic it may deliver and a change in the excitation of the synchronous motor efiects a corresponding 0 ange in its maximum pull out torque. When two machines of this character are operating together, a simultaneous change in field excitation of the two machines in a predetermined ratio efi'ects the kilowatt capacity of the system, orin other words, it causes a change in the stability of the system. In the event the excitation of the two machines is increased to maximum value in the same ratio as that determined for unity power factor operation, the maximum point of the system stability is provided.

As described hereinbefore, the control of the stability of the system ma be easily controlled by operating either 0 the field rheostats 33 and 34, to simultaneously lower or raise the excitation currents. An suitable instrument ma be utilized for in 'cating to the operator t e degree of stability of the system. Therefore, it is evident that only a sim 1e and comparatively easy adjustment is a 1 that is required of the operator in the event the ship is changed from low to hi h speed or vice versa. In many instances, t e cruising speed is low, which requires that the power system deliver a small amount of power, therefore, the field excitation may be adjusted to provide a low degree of stability, which causes the system to 0 rate more efliciently under light load condltions and as the load increases the degree of system stability ma be raised a corresponding amount,

which keeps the operating efliciency of the system at the highest possible valuethroughoutits range of operation.

' In reversing the operation of the ship, the ropulsion motor is required to deliver a high torque which, in many instances, is considerably greater than the torque required for ordinary operation. In order to rovide for increasing the pull out torque of e proller motor to its maximum value in pero reversing" o rations revision is made or short-circuit ing the fild rheostat 34 in response to the actuation of the control switch 23 to the reverse position. As shown, the resistance unit of the rheostat 34 is disposed to be shunted upon the closure of a relay 86, the energizing circuit of which is controlled by a contact member 87,provided on the control switch 23. It will be evident that when the motor field excitation is suddenly increased in this manner that the unity power factor conditions of the system no longer exist; However, in this instance, the importance of obtaining maximum torque of the propeller motor is greaterthan that of maintaining the operation of the system at unity power factor.

In view of the foregoing discussion, it is evident that by utilizing a pair of synchronous machines having substantially the same electrical characteristics and controlling the relative values of excitations of the two machines, that the most desirable power factor condition of the s stem may be automatical- It may be stated in conclusion that while the illustrated example constitutes a practical embodiment of my invention, I do not wish to limit myself strictly to the exact details herein illustratedv since modifications of the same may be made without dc arting from the s irit of the invention as defined in the a pen ed claims.

I 0 mm as my invention: 1. In a marine drive, in combination, a synchronous-propulsion motor, a synchronous generator for supplying power to the motor, means for driving the generator at a variable speed to control the s d of the ropulsion motor, said motor an generator ing provided with separately-excited field windings, and having substantially the same short-circuit charc'teristics, means for controlling the excitation of the machines, said means comprising a plurality of field rheostats independently operable to establish unity power factorconditions in the system, and means for efiecting simultaneous operation ofthe rheostats while maintaining their original relative positions for unity power factor op- .eration, whereby difierent degrees of excitation, in'the same ratio, may be obtained to establish different de recs of system stability in accordance wit the load imposed upon the motor and generator.

2. In a marine drive, in combination, a synlll . excited field winding, said motor 1mm I chronous motor provided with a se aratelyaving a predetermined short-circuit characteristic, a synchronous generator provided with a sep- 7 '5 arately excited field winding for supplying power to the motor, said generator having a short-circuit characteristic substantially the same as the motor, a prime mover for driving the generator, a source of current for energiz- 10 ing the field windings, means for independently "controlling the excitation of the generator and motor fieldwinding, said means being disposed to effect definite variations in the excitation current, and means for controlling the operation of said excitation controlling means-to efi'ect a simultaneous variation of the exciting currents in predetermined proportions, thereby, to maintain the internal voltages of the generator and motor in a constant predetermined relationship to preseparately excited field winding for supplying power to the motor, said generator having a short-circuit characteristic substantially the same as the motor, a switch for controlling the direction of operation of the motor, means for controlling the excitation of the generator and motor field windings, said means being disposed to eiiect predeten mined variations in the excitation of each machine simultaneously, to maintain continu- 40 one stability in the operation of the machines as the excitation is varied to suit the load con ditions, and means responsive to the directioncontrolling switch for controlling the motor excitation independently of the generator excitation for reversing operation, whereby the field of the motor is excited tea maximum in response to the operation of the said switch to the reverse position to provide maximum motor torque;

4. In a power-transmission system, in com bination, a synchronous motor which may be subjected to. a variable load, a synchronous generator set for supplying power-atvariahle voltage and frequency to the motor, said. generator and motor havin substantially the. same electrical characteristics adaptiu them for parallel operation, a source of cubic voltage power or exciting the generator and motor,-means for initially controlling the excitation of the machines, said means comrising means :Eorsubjecting the generator eldtora combination. of vo tages obtained from the excitation source and ,for connecting 4 the motor field to the source, and me '5 erable to ad ust the relative degrees f exmeans bein disposed to initially su citation of the machines to cause them to opcrate at unity power factor, said means being disposed for simultaneous operation, whereby the excitation of the mac ines may be increased or decreased to control the operating stabilit of the system in accordance with the loa variation of the motor.

5. In a power-transmission system, in combmation, a synchronous motor which may be subjected to a variable load, a synchronous generator set for supplyin power at variable voltage and frequency to t e motor, said gencrator and motor having substantially the same electrical characteristics adapting them for parallel operation, rheostatic means associated with each machine for initially ad'- justing the excitation of each machine independently of the other to obtain unity poweractor during the operation of the system, and means for jointly actuating said rheostatic means associated with each machine disposed to maintain said relative excitation of the motor and generator, whereby the unity power factor condition may be maintained regardless of changes in voltage and frequency of the stem.

6. ii an electric drive for ship propulsion, in combination, a propulsion motor provided with a field winding, a generator provided with a field windin for supplying power to the motor, said gene ator and motor having substantially the same short-circuit characteristics which enab es them to develop the same internal volta es for equal values of excitation, a double voltage supply for exciting the field windings, manually-operable means for controlling the connection of said field windings to the voltage supply, said ect the generator eld winding to double normal voltage to obtain a rapid voltage rise, and

manually operable means for controlling the exciting current in the field windin i said means being disposed to permit in ividual ad'ustment of the excitation currents and simultaneous adjustment thereafter to cause both machines to operate at substantially the same power factor and at a predetermined power factor regardless of the load variation on the system.

7. In an electric drive for ship propulsion, in combination, a propulsion motor provided with a field winding, a generator provided witha field winding for supplying power to the motor, said generator and motor having substantially the same short-circuit characteristics wh ch enables them to develop the same internal voltages for equal values of excitation, a rheostat disposed to control the excitation of each field winding and mechanical means for concurrently operating both rheostats to simultaneously vary the fieid excitation of the machines in predetermined to maintain a predetermined rela tive excitation of the two machines, whereby a predetermined ratio 'as t their internal voltages may be maintained in e load on the system changes in response to the desired movements of the 8. In an electric-ship propulsion system in combination, a synchronous generator dis- 4 posed to operate at variable frequency, a xsynchronous propulsion motor having subregardless o reverse operation of the ship.

stantially the same electrical characteristics as the generator, said motor being connected in (parallel circuit relation to the generator an subjected to the variable frequency generator voltage to vary its speed to control the speed of the ship, a source of excitation voltage for the enerator and motor and means for contro ling the excitation of the. machines, said means being disposed to permit individual adjustment of the excitation of the machines to establish a predetermined power-factor condition in the system and operable to thereafter simultaneously regulate the excitation of both machines to provide maximum stability and maintain the preselected power factor in their synchronous operation regardless of the load variation.

- 9. In an electric ship propulsion system, in combination, a synchronous generator dis-. posed to operate at variable frequency, a synchronous propulsion motor having substantially the same electrical characteristics as the generator, said motor being connected in (parallel circuit relation to the generator an subjected tothe variable frequency generator voltage to vary its s to control the speed of the ship, means or controlling the excitation of the machines, said means be- J the motor, said motor and generator having substantially the same short-circuit characteristics, means for driving the generator,

teams;

establish a predetermined war-factor condition, and means for mec anically connecting the rheostats together to provide for maintaining a predetermined relation between the field excitations to maintain a constant system power factor and system stabilit in accordance with the load being carried the system.

11. n a marine drive, in combination a synchronous generator havin a separatelyexcited field winding, a sync ronous motor provided with a separately-excited field winding disposed to be connected to the generator, a source of power for exciting the field windin s of the generator and motor, and means or simultaneously varying the excitation of the generator and motor field windin in redetermined proportions to maintain continuous stability in the operation of the machines as the excitation of the field windings is varied to meet load conditions, said means including individual means associated with each field winding independently operable to initiallyadjust the excitation of each machine independently of the other.

In testimony whereof, I have hereunto subscribed my name this 4th day of February,

WALTER SCHAELCIHJIN.

I. source of excitation for the motor and generator,- rheostats for va the separate excitation of the motor a dgenerator, a manually-operable controller for controllin themitial energization of the motor and generator, said controller bein disposed to render the rheostats efiective o y when actuated to a predetermined position, said rheostats being disposed for individual operation to the adiustment of the relative field excitations of e motor and generator to I 

